Frequently dying your hair has been linked to an increased risk of developing breast cancer.

Rachel Hosie, The Independent, Oct 16, 2017

According to a study by London surgeon Kefah Mokbel, women who colour their hair have a 14 per cent rise in rates of breast cancer.

Professor Mokbel, who works at the Princess Grace Hospital in Marylebone, London, advises that women dye their hair no more than two to five times a year.

He also recommends using as many natural products on their hair as possible, suggesting henna, beetroot or rose hip, The Sunday Times reports.

"What I find concerning is the fact that the industry recommends women should dye their hair every four to six weeks," Professor Mokbel said.

"Although further work is required to confirm our results, our findings suggest that exposure to hair dyes may contribute to breast cancer risk."

Professor Mokbel has also made clear that the link is merely a correlation: "The positive association between the use of hair dyes and breast cancer risk does not represent evidence of a cause-effect relationship," he wrote on Facebook.

And he explained further on Twitter:

Women are advised to reduce exposure to synthetic hair dyes to 2-6 times per year and undergo regular breast screening from the age of 40

Sanna Heikkinen from the Finnish Cancer Registry said separate Finnish research found a link between women who use hair dye and likelihood of developing breast cancer.

"We did observe a statistical association between hair dye use and risk of breast cancer in our study," she said.

But like Mokbel, Heikkinen stressed that scientists aren't certain of a cause-effect relationship though.

"It is not possible to confirm a true causal connection," she said. "It might be, for example, that women who use hair dyes also use other cosmetics more than women who reported never using hair dyes."

According to haircare professionals at the Cosmetic Toiletry and Perfumery Association, hair dyes are covered by robust safety requirements.